How can I set padding on category & product images?

Hi there does anybody know offhand where I can set the padding around the category and product images so that the text below them isn't shoved right up against them. I found some code

.productListing-data {
padding-top: 15px;
padding-bottom: 15px;
padding-right: 15px;
margin-right:1.5em;
border-bottom: 1px solid black;
}

However this appears to do nothing I can discern and certainly nothing regarding what I am trying to achieve although I am a noob and could easily be doing something very retarded. The stylesheet.css I am using has come from the template called Future Zen. To be honest I don't recognise most of the elemets that are referenced in it so I'm just guessing my way around. Does anybody know what I should be tweaking to alter the padding on these images? Any help would be greatly appreciated. Cheers.